Leaché Adam D, Davis Hayden R, Singhal Sonal
Department of Biology, University of Washington, Seattle, Washington, USA.
Burke Museum of Natural History and Culture, University of Washington, Seattle, Washington, USA.
Mol Ecol. 2025 Jul;34(13):e17819. doi: 10.1111/mec.17819. Epub 2025 Jun 4.
Coalescent modelling of hybrid zones can provide novel insights into the historical demography of populations, including divergence times, population sizes, introgression proportions, migration rates and the timing of hybrid zone formation. We used coalescent analysis to determine whether the hybrid zone between phylogeographic lineages of the Plateau Fence Lizard (Sceloporus tristichus) in Arizona formed recently due to human-induced landscape changes, or if it originated during Pleistocene climatic shifts. Given the presence of mitochondrial DNA from another species in the hybrid zone (Southwestern Fence Lizard, S. cowlesi), we tested for the presence of S. cowlesi nuclear DNA in the hybrid zone as well as reassessed the species boundary between S. tristichus and S. cowlesi. No evidence of S. cowlesi nuclear DNA is found in the hybrid zone, and the paraphyly of both species raises concerns about their taxonomic validity. Introgression analysis placed the divergence time between the parental hybrid zone populations at approximately 140 kya and their secondary contact and hybridization at approximately 11 kya at the end of the Pleistocene. Introgression proportions estimated for hybrid populations are correlated with their geographic distance from parental populations. The multispecies coalescent with migration provided significant support for unidirectional migration moving from south to north, which is consistent with spatial cline analyses that suggest a slow but steady northward shift of the centre of the hybrid zone over the last two decades. When analysing hybrid populations sampled along a linear transect, coalescent methods can provide novel insights into hybrid zone dynamics.
杂交带的溯祖模型可以为种群的历史种群统计学提供新的见解，包括分歧时间、种群大小、基因渗入比例、迁移率以及杂交带形成的时间。我们使用溯祖分析来确定亚利桑那州高原围栏蜥蜴（Sceloporus tristichus）系统发育谱系之间的杂交带是近期由于人为引起的景观变化而形成的，还是在更新世气候变化期间起源的。鉴于杂交带中存在另一个物种（西南围栏蜥蜴，S. cowlesi）的线粒体DNA，我们测试了杂交带中是否存在S. cowlesi核DNA，并重新评估了S. tristichus和S. cowlesi之间的物种界限。在杂交带中未发现S. cowlesi核DNA的证据，并且两个物种的并系性引发了对其分类有效性的担忧。基因渗入分析表明，亲本杂交带种群之间的分歧时间约为14万年前，它们在更新世末期的二次接触和杂交时间约为1.1万年前。估计的杂交种群的基因渗入比例与其与亲本种群的地理距离相关。具有迁移的多物种溯祖模型为从南向北的单向迁移提供了有力支持，这与空间渐变分析一致，空间渐变分析表明在过去二十年中杂交带中心缓慢但稳定地向北移动。在分析沿线性样带采样的杂交种群时，溯祖方法可以为杂交带动态提供新的见解。
